Method for Treating Lignocellulosic Parts

ABSTRACT

A method for treating lignocellulosic parts for producing foamed or foam-like parts, including: drying the lignocellulosic parts, the drying involving removing water, wherein the drying is achieved by applying at least one liquid drying agent that dissolves and/or at least partly replaces the water, wherein preferably the drying agent is a swelling agent for lignocellulose; and chemical modification, by etherification of the dried lignocellulosic parts; wherein the chemical modification is such that a volume of the lignocellulosic parts is increased by at least 25% with respect to an initial volume of the parts.

FIELD

The invention relates to a method for treating lignocellulosic parts, for example wood parts or bamboo parts.

INTRODUCTION

Synthetic polymeric foams can be described as materials composed of a gas phase trapped in a solid matrix. Thus, they are two-phase systems commonly characterized by their low density.

The foam market was established during the past century thanks to the progress achieved on polymer technology. Solid foams are lightweight materials, used by the building sector mainly as thermal insulators in the core of sandwich structures. Advances on thermoplastic and thermosetting materials contributed significantly to the development of the polymeric foam industry. However, environmental issues changed the direction of development in order to find alternative materials and technologies with lower environmental impact. New regulations and international agreements—e.g. Montreal protocol and Kyoto protocol—are setting challenges to the polymer industry, which tends to replace products from fossil resources by biobased products.

In that respect, forest resources have been taken into account as alternative materials to replace petroleum derivatives. In particular, lignocellulosic materials are promising candidates since they are abundant and biodegradable natural polymers. In the last decades, research efforts were devoted to develop wood plastic composites (WPC) with the aim of diminishing the use and load of synthetic polymers, reducing the cost of the final material, and eventually improving the material properties.

So far, WPCs have been processed and used to create foams following the standard technologies that are traditionally used to produce foams out of synthetic polymers. As a result, a big variety of WPC foams were manufactured introducing lignocellulosic fibers or flour as a filler of reinforcement of the main material matrix.

For example, German Offenlegungsschrift DE2059625 discloses a method, wherein strong foamed products, with low bulk weight, flame retardancy and water repellent properties are obtained by soaking wood (pref. birch or alder) with a reactants for a polyurethane reaction. The known method requires water in the wood for the reaction. During the process, CO₂ gas is formed in the wood. Only a little amount of water is used, to prevent overproduction of CO₂ which damages the wood structure. The reaction can be followed via foam which comes about at the wood-ends. The resulting product has an open cell structure, being less capable in storing water. Also, the wood is internally dead and has a structure similar to polyurethane foam, having a dense cell structure. According to DE'625, silicones or waxes can be added to confer water repellency, and paraffin oil for the same purpose and also to control pure size and prevent cracking of the wood. The process is relatively hard to control, requiring a particularly amount of diisocyanate depending on the hydroxyl groups of wood celluloses (which acts as a polyalcohol in the bonding reaction of the polyurethane). Also, the known process involves the use of polyurethane, which has become controversial from the environmental point of view.

It is known that hydrophilic properties of lignocellulose materials influence the biological stability and durability of the final product. Various wood modification methods are known from the prior art, such as thermal and chemical modification methods, to improve the biological stability and durability. Chemical modification can achieve much more than thermal modification since properties can be achieved by choosing specific molecules that are added to the lignocellulosic material. For all existing processes there are some drawbacks. High costs for production is one of them. Also in the functionalizations there is still room for improvement. The ester bond in acetylated wood, for instance, has the inconvenience that it can be hydrolyzed in alkaline conditions. Esterification of wood, —as well as other chemical treatments—results in by-products that reduce the efficiency and increase the labor of the modification process.

A known modification process is etherification using epoxides. An ether bond could perform better than an ester bond since it is not hydrolysable as an ester. The reaction between epoxides and hydroxyl groups of the wood involves an initial reaction of a hydroxyl group and an epoxide molecule, generating an ether derivative that contains a new hydroxyl group. This new OH— group will be available for further reaction with another epoxide molecule giving rise to polymerization. The etherification reaction as such can be base or acid catalyzed and, most important; it does not produce by-products, which is a big advantage with respect to other chemical modifications. The ideal catalyst for this purpose should be effective at low reaction temperatures, easily removed after reaction, nontoxic and noncorrosive. Good candidates are weakly alkaline compounds.

However, all chemicals able to react with the hydroxyl groups of the wood cell wall can also react with the water that is naturally available in the wood structure. Epoxides are no exception and the reaction of an epoxide with water results in formation of glycol, oligomers and polymers as by-products. On the one hand, the water consumes an unacceptably high amount of epoxides from the point of view of commercial applications of a process. Furthermore, the by-products can be difficult to separate and regenerate to get the initial reagents at industrial scale.

U.S. Pat. No. 3,406,038 discloses a drying step and a subsequent chemical modification step. It discloses a wood treatment method, for improving dimensional stability of the wood a polyhydric alcohol, then impregnating the wood with an alkylene oxide, and effecting the reaction of these substances with water itself. Wood drying can be carried out during the treatment of the wood with the polyhydric alcohol and thereafter, so that the wood “does not become warped”.

GB814,584 discloses a method for stabilizing of wood. The method involves impregnation with a phtlalaldehydic acid compound, swelling with a liquid swelling agent (for example an organic solvent), and curing by heating while in the swollen condition.

SUMMARY

The present invention aims to provide an improved method for treating lignocellulosic parts. Particularly, the method aims to provide a more efficient and economical method, to produce relatively lightweight (preferably foamed or foam-like) lignocellulosic parts that can be used as insulation material, the resulting material being durable, and preferably water repellent.

According to the invention, these and other aspects are achieved by a method that includes:

-   -   drying the lignocellulosic parts, the drying involving removing         water,

wherein the drying is achieved by applying at least one liquid drying agent that dissolves and/or at least partly replaces the water, wherein preferably the drying agent is a lignocellulosic part swelling agent;

and

-   -   chemical modification, preferably etherification, of the dried,         preferably swollen, lignocellulosic parts.

According to a preferred embodiment the chemical modification is such that a volume of the lignocellulosic parts is increased by at least 25% with respect to an initial volume of the parts.

The inventors have found that, surprisingly, chemical modification (particularly by etherification) of the dried lignocellulosic parts can lead to a significant volume increase of the material. Also, it has been found that the resulting material is relatively lightweight, has a foam-like structure, and can therefore be used as insulation material. Also, the resulting material can be very durable (that is: insensitive to micro organism related decay), and water repellent. Particularly, the present invention can be carried out using relatively large lignocellulosic parts, for example having at least one dimension (length, width) larger than 1 mm, for example larger than 1 cm. Also, smaller lignocellulosic parts can be treated, for example separate lignocellulosic particles, fibres, or powder.

The above-mentioned etherification can include reaction of momomers with lignocellulose and polymerisation from monomers, the resulting reaction products being bound to lignocellulosic components. The etherification involves the direct reaction of lignocellulosis with chemicals. This gives a very stable modification.

Good results are obtained in case the etherification involves subjecting the lignocellulosic parts to a reactant and a catalyst, the reactant and catalyst being supplied in a weight ratio to (significantly) expand the lignocellulosic parts. For example, the lignocellulosic parts can be impregnated with a mixture of the reactant and catalyst (in the weight ratio selected to achieve the expansion of the parts), to carry out the etherification of the parts.

For example, it has been found that the catalyst can be supplied in such a large amount (with respect to the amount of reactant used) that a resulting etherification reaction (having a respective high reaction rate) leads to the above-mentioned high volume increase (of at least 25%). More particularly, it is believed that the use of a relatively large amount of catalyst leads to a respective, relatively high reaction rate, which surprisingly leads to a foaming of the lignocellulosic parts.

Therefore, it has been found that the reactant and catalyst can be supplied in such a ratio that the resulting etherification of the lignocellulosic increases the volume of the parts by at least 25% with respect to an initial volume of the parts.

For example, a weight ratio reactant:catalyst used can be 99:1 or smaller. For example, a weight ratio reactant:catalyst used can be in the range of 90:10 to 99-1. In an embodiment, good epoxide based etherification results are achieved using propylene oxide (PO) as reagent and di-methyl ethyl amine (DMEA) as catalyst, with a weight ratio PO:DMEA of 97:3.

Preferably, the drying agent is a non-hydroxylic drying agent, particularly a non-hydroxylic liquid drying agent. For example, the invention makes use of at least one non-hydroxylic solvent, which removes water from the lignocelluloses, thereby not only preventing shrinking of the wood, but also minimizing by-product formation. Also, unnecessary consumption of reagents that would take place when water is present, can be prevented.

Particularly, the initial volume of the parts is a cumulative initial volume of the lignocellulosic parts (i.e., a total volume that is occupied by the parts before the treatment). The significant (cumulative, total) volume increase as such involves a significant decrease of the density (kg/m³) of the material.

Particularly, it has been found that chemically modifying lignocellulose—for example by etherification with epoxides—can induce expansion of the lignocellulose structure to the extent of producing a lightweight material with the characteristics of solid polymeric foams. In addition, the final product is less hydrophilic than the untreated lignocellulosic material, making it more resistant in moist environments.

According to a further embodiment, the volume of the lignocellulosic parts is increased by 100% or more, for example by 400% or more. Particularly, the modification can be such that the lignocellulosic parts rupture (during/due to the expansion thereof).

Also, for example, the lignocellulosic parts to be treated can have an initial density (kg/m³), wherein the modification is such that the density of the lignocellulosic parts is lowered with respect to the initial density, for example by a factor of at least one half (½) and more particularly a factor of two or more. Experiments have been carried out, wherein the density of the material was decreased by a factor of more than 3

The chemical modification can include reaction of momomers with lignocellulose and polymerisation from monomers, the resulting reaction products being bound to lignocellulosic components. According to a further embodiment, the modification can be an epoxide based etherification.

As follows from the above, the modification may involve subjecting the lignocellulosic parts to a reactant and a catalyst, the reactant and catalyst being supplied in an amount to expand the lignocellulosic parts. Good results have been obtained in case the catalyst is di-methyl-ethyl-amine (DMEA). Also, tri-methyl-amine (TMA) is expected to provide good results.

According to an embodiment, the modification can involve subjecting the lignocellulosic parts to an alkylene oxide, for example 1,2-butylene oxide, propylene oxide, or styrene oxide.

Other candidates to be used for the modification of the wood are for example: a glycidyl ether, for example allyl glycidyl ether, phenyl glycidyl ether, glycidyl 4-nonylphenyl ether; epoxidized unsaturated fatty acids and their derivatives, for example esters.

According to a further embodiment, the drying can include:

a) subjecting the lignocellulosic parts to the drying agent, particularly to impregnate the lignocellulosic parts with that drying agent to dissolve and replace water;

b) removing at least part of the drying agent from the lignocellulosic parts, and preferably only part of the drying agent, for example to the extent that a remaining amount of drying agent provides swelling of the lignocellulosic parts;

c) optionally repeating steps a) and b).

Advantageously, the drying can involves saturating the lignocellulosic parts with the drying agent.

It has been found that, particularly in case the modification is an etherification of the lignocellulosic parts, relatively little (almost no) reaction by-product is available in the modified lignocellulosic parts. According to an embodiment, at least part of the drying agent can be left in the lignocellulosic parts to maintain a certain swollen state of the lignocellulosic parts, until (and preferably during) the subsequent modification step.

In an embodiment, the present invention presents a method to etherify solvent-dried lignocellulosic material.

According to a preferred, efficient embodiment, the drying agent already includes or is a reagent for modification of the lignocellulosic parts. As follows from the above, the drying of the lignocellulosic parts is preferably a separate step, which does not yet lead to a chemical modification of the lignocellulosic parts. Thus, during the drying, the reagent is preferably chemically inactive, e.g. it does not yet modify the lignocellulosic parts, but only mixes with water to remove the water from the lignocellulosic parts. The modification step can include the further application of a catalyst, to initiate a reaction between the lignocelluloses and the reagent.

According to an advantageous elaboration, the drying and modification are carried out in the same treatment chamber or vessel, for example a reactor chamber. In this way, the condition of the lignocellulosic parts can be controlled accurately throughout the process, for example the content of a drying (swelling) agent in the lignocellulosic parts, temperature and pressure. Optionally, in this way, the lignocellulosic material can be maintained in a constantly swollen state by a water replacing swelling agent, prior to the modification thereof.

According to non-limiting embodiments, the drying agent can be selected from the group consisting of a non-hydroxylic solvent, an organic solvent, for example EGDME (Ethylene glycol dimethyl ether), propylene oxide, butylene oxide, THF (tetrahydropyran), acetone, small ketones, MEK (methyl ethyl ketone).

According to an embodiment, the drying agent is a solvent. Optionally, the drying agent is a swelling agent for (the polar/hydrophilic) wood, for example with at least 10% (estimate) of the swelling power of water (and thus are polar/hydrophylic enough to dissolve enough water from the wood). Optionally, the solvent drying agent may provide a flexibilizing effect.

The solvent can serve to make the lignocellulosic parts accessible for reagent molecules (and/or catalysts), which have too low polarity/hydrophilicity and/or too large size to swell/enter the lignocellulosic parts sufficiently themselves. A solvent drying agent can also serve to remove a reagent and/or catalyst after the modification reaction.

Also, according to a preferred embodiment, the drying agent is sufficiently volatile to be removed easily from the lignocellulosic parts after the process.

None-limiting examples of the drying agent are.

-   -   the lower epoxides propylene oxide and butylene oxide themselves         (without catalyst), if used subsequently as reagent (in presence         of catalyst); this opens possibilities for very simple and         attractive processes;     -   polar lower ethers, like ethylene glycol dimethylether (EGDME),         tetrahydrofuran (THF) etc;     -   lower ketones, like acetone, methylethylketone etc.;     -   lower esters, like methyl-, ethyl-, propyl- and isopropylacetate         etc.

Preferably, the liquid drying agent has substantially the same order of magnitude of lignocellulosic parts swelling capabilities as wood swelling capabilities of water.

Good results have been obtained in case the water content of the lignocellulosic parts is lower than 5 w %, preferably lower than 3 w %, more preferably lower than 1 w %, after the drying and before the modification is started. A swelling agent (if any) content of the lignocellulosic parts can be significantly higher than 1 w % after the drying and before the modification is started, to counteract the removal of water.

The present invention further provides an insulating element, comprising one or more lignocellulosic parts produced by a method according to the invention. For example, the element can be configured to provide thermal insulation, sound insulation, or both. The insulating element can be, or be part of a construction element. For example, the insulating element can be plate material, a wall or wall part, a laminate, a sandwich construction, a construction block, a beam, door, a window, window casing, ceiling part, board, floor part, chipboard, roof boxes and/or the like.

The insulating element can be completely manufactured from the treated lignocellulosic parts provided by the invention. In addition, the insulating element can contain one or more different materials, for instance wood, metal, plastic or a combination of these or other materials. In the latter case, the material manufactured by the method according to the invention can be processed into the element in different manners.

The treated lignocellulosic parts can, for instance, be surrounded by other material and/or extend on a surface of the insulating element. The lignocellulosic parts can be used to cover a surface of an element, for example partly or completely. The insulating element can be provided with, for instance, at least one layer of the expanded lignocellulosic material and at least one layer of another material (mentioned above).

Further advantageous embodiments are described in the dependent claims. The invention will now be explained with reference to the non-limiting examples and the drawing. Therein shows:

FIG. 1 a flow chart of an embodiment of the invention.

As is depicted in the drawing, the present example of a method for treating lignocellulosic parts can include providing the lignocellulosic parts (step 100), a step 101 of drying the lignocellulosic parts (the drying involving removing water from the wood), and a step 102 of chemical modification of the dried lignocellulosic parts. Non-limiting examples include etherification (as will be described below).

Various types of lignocellulosic parts can be treated by the process, for example powder, flour, fibres, chips, chunks, blocks, laths, planks, beams, and/or other parts. For example, a smallest external dimension of each of the lignocellulosic parts can be larger than 1 mm, for example larger than 1 cm. A length of each of the lignocellulosic parts can be larger than 1 mm, for example larger than 5 cm, for example larger than 1 m (particularly in case of commercial wood modification). The mass of each of the lignocellulosic parts can be larger than 0.001 kg, for example larger than 0.01 kg, particularly larger than 0.1 kg, for example larger than 1 kg (for example: larger than 10 kg). The lignocellulosic parts can be freshly cut parts, or it they can be pre-treated (for example conditioned) before the drying step 101 is carried out. The lignocellulosic parts can also be small parts, for example flour, grains or fibers. According to a further elaboration, a water content of the lignocellulosic parts that is provided (step 100) can be higher than 5 w %, for example about 8-10 w %, or higher (for example over 25 w %).

Drying

The drying step 101 can be carried out, for example, in a treatment chamber that can be sealed from an environment, for example a reactor. The drying step 101 can include the use of one or more drying agents (for example a mixture of at least two drying agents), to extract water from the lignocellulosic parts. Advantageously, the drying agent used in the drying step 101 acts as a wood swelling agent. Also, advantageously, the liquid drying agent dissolves and/or at least partly replaces the water (i.e. mixes with water). Optionally, the process can be carried out in such a manner, that the lignocellulosic parts are all still swollen by an amount of liquid drying agent (left in the lignocellulosic parts after the drying step 101) when the parts are processed in the modification step. In particular, the amount of liquid drying (swelling) agent that is present in the lignocellulosic parts after the drying step 101 counteracts shrinkage of the parts.

According to a further non-limiting embodiment, the liquid drying agent has substantially the same order of magnitude of wood swelling capabilities as wood swelling capabilities of water. Alternatively, the liquid drying agent can have a wood swelling capability that is higher or lower than the wood swelling capability of water, for example higher or lower by a factor in the range of 0.1-1.5

At least up to the modification step 102, the lignocellulosic parts can continuously contain swelling agent that swells the lignocellulosic parts: first the swelling agent water (before the drying step 101), and subsequently the drying agent that replaces the water and has swelling capabilities.

Subjecting the lignocellulosic parts to drying agent (for providing water extraction and replacement) can be achieved in various ways. According to a preferred example, the drying simply involves saturating the lignocellulosic parts with the drying agent. Also, for example, the lignocellulosic parts can be immersed, sprayed or rinsed with liquid drying agent, during a predetermined drying period, to achieve water removal. The drying can involve providing a bath of liquid drying agent, and laying or submersing the lignocellulosic parts in the bath. According to a further example, water that is extracted from the lignocellulosic parts by liquid drying agent is removed from the drying agent, via a separation step 106. Drying agent that is recovered in step 106 can be reused in the drying of the lignocellulosic parts (step 101).

Preferably, during the drying step 101, the liquid drying (i.e. swelling) agent totally penetrates the lignocellulosic parts, to reach any water that may be present in the lignocellulosic parts (to dissolve, remove and replace the water), and to provide uniform distribution of drying agent induced (optional) swelling. More particularly, the drying step 101 can include:

a) subjecting the lignocellulosic parts to the drying agent, particularly to impregnate the parts with that drying agent to dissolve and replace water;

b) removing at least part (for example only part) of the drying agent from the parts, such that a remaining amount of drying agent (left in the lignocellulosic parts) still provides a certain swelling of the lignocellulosic parts to prevent rupture of the parts;

c) optionally repeating steps a) and b).

Removing drying agent to extract water (step b)) can be accomplished in various ways. Step b) can include removing drying agent that is present outside the lignocellulosic parts (for example draining a bath of drying agent that soaks the lignocellulosic parts). Also, step b) can include removing part (not all) of drying agent that is present in the lignocellulosic parts.

At least part of the step b) of removing the drying agent can include discharging liquid drying agent from the treatment chamber, for example using a discharge pump. Also, at least part of that step b) can be carried out under sub-atmospheric pressure, and a temperature in the range of 0-200° C. The pressure and temperature can be such that drying agent (containing dissolved water) evaporates from the lignocellulosic parts. Said sub-atmospheric pressure can be a pressure lower than 0.5 bar, for example about 0.1 bar.

The subjecting lignocellulosic parts to the drying agent (step a)) can be achieved under a predetermined pressure and a temperature in the range of 0-200° C., suitable for the drying agent to penetrate the lignocellulosic parts. For example, during step a), the pressure in the drying chamber can be atmospheric pressure, or higher, for example an elevated pressure with respect to the pressure during removal of the drying agent.

Steps a-c can be carried out such, that resulting lignocellulosic parts have a desired low water content. Particularly, after the drying step 101 and before the modification is started, the water content of the lignocellulosic parts is lower than 5 w %, preferably lower than 3 w %, and most preferably lower than 1 w %.

Also, the resulting lignocellulosic parts still contain liquid drying agent, acting as a swelling agent (having replaced the water during the drying step). For example, the content of the drying agent can be higher than 1 w % after the drying step 101 (and before the modification is started).

Various drying agents, having lignocellulosic parts swelling capabilities, can be used (as is mentioned above). A preferred drying agent is a volatile drying agent (for example being volatile at room temperature, 22° C., and atmospheric pressure), capable to remove a non-volatile liquid (i.e. being substantially not volatile at room temperature, 22° C., and atmospheric pressure, such as water) from the lignocellulosic parts, for example a polar solvent (other than water) that can dissolve water. In case of etherification, the drying agent can be selected from the non-limiting group of compounds of an organic (polar) solvent, for example EGDME, propylene oxide, butylene oxide, THF, acetone, small ketones, MEK (methyl ethyl ketone). In a further embodiment, the drying agent can include a reagent for modification of the lignocellulosic parts. Propylene oxide is an example of a swelling solvent that can provide both lignocellulosic parts drying and chemical modification (after application of a catalyst). Besides, a solvent drying agent can be used for the extraction of substances from the lignocellulosic parts, after the modification step.

Modification

The drying step 101 and chemical modification step 102 are preferably carried out in the same treatment chamber. The chamber preferably remains closed from an environment during the drying step 101, during the modification step, and an intermediate period (if any). Thus, the lignocellulosic parts—for example containing swelling agent which swells the parts—can remain in the treatment chamber throughout the process, so that a certain swollen state of the lignocellulosic parts can be controlled well.

The thus obtained dried lignocellulosic parts (provided by the drying step 101) can be directly used in the modification step 102 as indicated by arrow I in the drawing).

Part of the liquid drying agent can be recovered from the lignocellulosic parts in an intermediate step 105, before the lignocellulosic parts is subjected to the modification step. The recovery of part of the drying agent can be carried out such, that the resulting lignocellulosic parts still contains an amount of drying agent acting as swelling agent, which amount is sufficient to prevent collapse of the lignocellulose structure, which may influence the efficiency of the modification in step 102.

Any drying agent that is left in the lignocellulosic parts (after the drying step 101 and optional recovery step 105) can enhance penetration of reagent, catalyst, or both, during the modification step 102.

The modification step 102 can be carried out in different ways. According to a further embodiment the modification can include the use of at least one non-swelling reagent and a swelling agent. Alternatively, the modification can include the use of at least one swelling reagent, used as a drying agent in the drying of the wood. Also, as an alternative, the modification can include the use of at least one swelling agent acting as reagent, and at least one swelling agent that is not a reagent.

Advantageously, the chemical modification is such that a volume of the lignocellulosic parts (i.e. a total external volume, occupied by the parts) is increased by at least 25% with respect to an initial volume of the parts (leading to a significant density reduction of the material), for example 50% or more. In a preferred embodiment, the volume of the lignocellulosic parts is increased by 100% or more, for example by 400% or more. Also, the modification is such that the density of the lignocellulosic parts is lowered with respect to the initial density, for example by a factor of at least 50%. For example, it has been found that the weight ratio catalyst:reactant can be selected such that the afore-mentioned volume increase (and a respective density decrease) is achieved.

To this aim, it has been found that the chemical modification can proceed relatively fast and/or exothermic. Thus, a foam-like modified wood can be obtained, which can for example be used as an insulation material (for example as or as part of an element having thermally insulating properties).

In experiments described below, the modification step 102 is an epoxide based etherification. To this aim, the modification can involve subjecting the lignocellulosic parts to a reactant, for example an alkylene oxide, for example propylene oxide. Other candidates have been mentioned above.

Particularly, the modification can involve subjecting the lignocellulosic parts to the reactant and a catalyst. Good results have been obtained by using di-methyl ethyl amine (DMEA) as a catalyst, in combination with propylene oxide as a reactant. It is expected that tri-methyl-amine (TMA) will also provide improved results (for example with propylene oxide as a reactant).

The modification, for example etherification, is preferably carried out at a temperature in the range of 50-200° C. Also, good results can be achieved in case the modification is carried out at a pressure in the range of 1-20 bar, for example a pressure of about 1 bar or higher, for example a pressure higher than 5 bar, more particularly a pressure of about 9 bar. Preferably, the pressure is lower than 20 bar (for example lower than 15 bar).

The modification step 102 can be followed by a recovery step 103, to recover compounds (for example reagent, swelling agent, and/or catalyst) from the treatment chamber. The recovery step can include drying the lignocellulosic parts (to remove liquids there-from).

For example, a solvent can be used to extract one or more substances from the lignocellulosic parts after the modification step 102. In an embodiment, such extraction is carried out in the same treatment chamber, as was used in the modification step 102.

Preferably, the lignocellulosic parts are dried (in a further drying step 104) after the modification step 102 (and/or recovery step). This further drying step 104 can include various drying methods, for example oven drying, gas drying, or a different method. Preferably, recovered drying (i.e. swelling) agent is stored, to be reused in a subsequent wood treatment process.

Experimental Results

Experiments have been carried out using the above-described process. The treatment that is described in this example comprises solvent-drying the lignocellulosic material (in this case wood), followed by reaction of the water-free lignocellulosic material with an epoxide in the presence of a small molecule catalyst at desired temperature and pressure.

Particularly, Pinus sylvestris L. sapwood was tested, both in the form of slices and chips. For convenience, slices of the wood had been cut with approximate dimensions 30 mm×30 mm×10 mm. The samples had been carefully selected and no growth disturbances (e.g. knots, resin pockets, etc.) have been included in the test material.

The wood was carefully planed parallel to the tangential or the radial plane, thus allowing for measurement of dimensions 100% radial or tangential. Prior to treatment the wood has been acclimatised in a specified climate (i.e. 65% r.h. at 20° C.) to achieve a specific starting moisture content, which was found to be 12%.

Samples were weighed on a balance to the nearest 0.01 g before and after treatment. Additionally, the three dimensions of the sliced samples were measured before and after treatment with a calliper to the nearest 0.1 mm.

First, the samples were solvent-dried (step 101), included removing the water content of the lignocelulosic material by means of a solvent. The solvent was able to swell and penetrate the lignocellulosic material, it was inert, and dissolved the water in order to extract it. The boiling point of the solvent is relatively lower (for example lower than 100° C. at atmospheric pressure, in a further embodiment lower than 80° C. at atmospheric pressure) to facilitate later removal. In the present experiment, the samples were solvent-dried up to <3% water content using pure propylene oxide as drying agent, in a stainless steel 1 l reactor, at 10 bars and 120° C.

Subsequently, an etherification (step 102) of the samples was carried out using a mixture of propylene oxide (PO) as reagent and di-methyl ethyl amine (DMEA) as catalyst; the substances were present in the mixture with a weight ratio PO:DMEA of 97:3. The wood was impregnated with this mixture after the afore-mentioned pure drying agent (pure PO) had been removed (i.e. recovered in a step 105) from the wood.

For all reactions, the afore-mentioned stainless steel 1 l reactor has been used. The wood parts were piled up in a mesh cage and separated with wire meshes. The slices were secured to prevent floating.

In the experiments, both drying the wood (step 101) and the etherification (step 102) have been carried out by means of respective two consecutive impregnation steps in the same reactor.

A typical impregnation process consisted of a pre-vacuum of about 30 min at 10 kPa, filling of the reactor, either with the drying agent to carry out step 101 or with the solution of reagent and catalysts (up to maximum 80% of the reactor volume) to perform subsequent step 102, application of pressure by adding nitrogen gas up to desired pressure, and heating up, maintaining the temperature for a specified time, cooling down, draining and applying a post vacuum using a cold trap to prevent liquids from going into the vacuum pump. The pressure, the temperature inside the reactor and the temperature of the heating oil have been monitored at intervals of maximum 15 min. At the end of the reaction (step 102) the treated wood samples have been weighed and the dimensions measured.

The temperature was chosen to be as high as possible in order to increase the reaction yield. Pressure could be chosen between 0 and 15 bar, and it was typically around 8 bar.

The treatment temperature was chosen to be as high as possible in order to increase the speed and reaction yield but preferably not higher than 120° C., which is a safe upper limit to minimize wood degradation. In the examples that are described below the temperature was set to 90° C. and the maximum pressure achieved during the process in the reactor was 9 bar.

Table 1 below provides results of the experiment. The chemical modification has lead to a significant volume increase of the wood parts (in some cases of more than 400%), and a significant respective density reduction. Also, the equilibrium moisture content (EMC) of the wood parts has significantly decreased (from about 14% to 8%). The wood parts were found to be water repellent, and had a foam-like structure.

TABLE 1 Overview of experimental results achieved after treatment of solvent-dried lignocelluloses modified with PO/DMEA. Density before Density after EMC before EMC after Lignocellulose treatment treatment treatment (% treatment material (Kg/m³) (Kg/m³) water) (% water) Pinus sylvestris 588 172 14.2 8.0 L. sapwood slices

Although illustrative embodiments of the present invention have been described in greater detail with reference to the accompanying drawings, it is to be understood that the invention is not limited to these embodiments. Various changes or modifications may be effected by one skilled in the art without departing from the scope or spirit of the invention as defined in the claims. It is to be understood that in the present application, the term “comprising” does not exclude other elements or steps. Also, each of the terms “a” and “an” does not exclude a plurality. Any reference sign(s) in the claims shall not be construed as limiting the scope of the claims. Also, for example, the term “wood” should be interpreted broadly; a “wood part” can be or include a lignocellulosic part. 

1. A method for treating lignocellulosic parts for producing foamed or foam-like parts, including: drying the lignocellulosic parts, the drying involving removing water, wherein the drying is achieved by applying at least one liquid drying agent that dissolves and/or at least partly replaces the water, wherein preferably the drying agent is a swelling agent for lignocellulose; and chemical modification by etherification, of the dried lignocellulosic parts; wherein the modification involves subjecting the lignocellulosic parts to a reactant and a catalyst, the reactant and catalyst being supplied in an amount to expand the lignocellulosic parts, wherein the chemical modification is such that a volume of the lignocellulosic parts is increased by at least 25% with respect to an initial volume of the parts.
 2. The method according to claim 1, wherein a water content of the lignocellulosic parts is lower than 5 w %, preferably lower than 3 w %, after the drying and before the modification is started.
 3. The method according to claim 1, wherein the modification is an epoxide based etherification.
 4. The method according to claim 3, wherein the catalyst is a tertiary amine, for example di-methyl-ethyl-amine (DMEA).
 5. The method according to claim 4 wherein the catalyst is tri methyl amine (TMA)
 6. The method according to claim 1, wherein the modification involves subjecting the lignocellulosic parts to an epoxide, such as an alkylene oxide, for example propylene oxide.
 7. The method according to claim 1, wherein a volume of the lignocellulosic parts is increased by 100% or more,
 8. The method according to claim 1, wherein a volume of the lignocellulosic parts is increased by 400% or more.
 9. The method according to claim 1, wherein the lignocellulosic parts to be treated have an initial density (kg/m³), wherein the modification is such that the density of the lignocellulosic parts is lowered with respect to the initial density, for example by a factor of at least 50%.
 10. The method according to claim 1, wherein the drying includes: a) subjecting the lignocellulosic parts to the drying agent, particularly to impregnate the lignocellulosic parts with that drying agent to dissolve and replace water; b) removing at least part of the drying agent from the lignocellulosic parts, for example such that a remaining amount of drying agent provides swelling of the lignocellulosic parts; c) optionally repeating steps a) and b).
 11. The method according to claim 1, wherein the drying involves saturating the lignocellulosic parts with the drying agent.
 12. The method according to claim 1, wherein the drying agent is selected from the group consisting of an organic solvent, propylene oxide, butylene oxide, lower ethers, ethylene glycol dimethylether (EGDME), tetrahydrofuran (THF), small ketones, acetone, MEK (methylethyl ketone), lower esters, methyl-, ethyl-, propyl- and isopropylacetate.
 13. The method according to claim 1, wherein at least part of the drying is carried out under subatmospheric pressure, for example a pressure lower than 0.5 bar, for example about 0.1 bar.
 14. The method according to claim 1, wherein a water content of the lignocellulosic parts is lower than 1 w %.
 15. An insulating element, comprising one or more foamed or foam-like parts produced by the method of claim
 1. 16. The insulating element of claim 15, wherein a water content of the lignocellulosic parts is lower than 5 w %, preferably lower than 3 w %, after the drying and before the modification is started.
 17. The insulating element of claim 15, wherein the modification is an epoxide based etherification.
 18. The insulating element of claim 17, wherein the catalyst is a tertiary amine, for example di-methyl-ethyl-amine (DMEA).
 19. The insulating element of claim 18, wherein the catalyst is trimethyl amine (TMA)
 20. The insulating element of claim 15, wherein the modification involves subjecting the lignocellulosic parts to an epoxide, such as an alkylene oxide, for example propylene oxide. 